The lie angle of a club head is the angle between the center line of the hosel bore and the groundline at a point tangent to the center line of the club head base.
If the toe of a right-handed club head is tilted up at the moment the club head face impacts a ball, the face will be aimed to the left and the ball will thus travel to the left of its intended path of travel. Conversely, if the toe of a right-handed club head is tilted down, i.e., if the heel is tilted upwardly, the shot will go to the right.
The angle of the face of course determines the loft of the club head; the greater the loft, the more off the target line the face will be at impact if the club is not held at the proper lie angle. If a golfer uses a club having a shaft that is too long for that golfer, the golfer will tend to raise the toe of the club head and thereby make an off target shot. Conversely, if a club shaft is too short for the golfer, the heel of the club will be raised and an off target shot in the opposite direction will occur. Thus, every club in a golfer's bag should be of a length that allows the golfer to hold the club so that the line tangent to the sole of the club head is parallel to the groundline.
However, there are no satisfactory means for determining whether or not a particular club having a known lie angle is being held improperly by the golfer. Of course, bad shots will indicate an improper holding of the club, but no training or practice aids are known to exist that will teach the golfer how to hold the club properly.
Significantly, the art teaches a trial and error approach to the correction of a golfer's swing. A common technique is to have the golfer make repeated swings at a ball on a plywood surface; a mark is placed on the sole of the club head and after a swing has been completed the mark is examined for scuff marks in a effort to determine if the golfer was holding the toe or the heel of the club too high, and if so, by how much.
Thus, there is a need for a device that enables a golfer to determine when a club is being held properly, but the prior art neither teaches nor suggests how such a device could be supplied.